Apply spotless. Fix esplugin application.

build.gradle

@@ -1,8 +1,4 @@
 
-// This plugin's version (typically must match that of ES).
-version = '7.9.2'
-group = 'org.carrot2'
-
 buildscript {
   ext {
     version_es = '7.9.2'
@@ -22,9 +18,16 @@ buildscript {
 plugins {
   id 'java-library'
   id 'idea'
-  id 'elasticsearch.esplugin'
+  id 'com.diffplug.gradle.spotless' version "4.5.1" apply false
 }
 
+apply plugin: 'elasticsearch.esplugin'
+apply from: file('gradle/validation/spotless.gradle')
+
+// This plugin's version (typically must match that of ES).
+version = '7.9.2'
+group = 'org.carrot2'
+
 repositories {
   mavenLocal()
   mavenCentral()

gradle/validation/spotless.gradle

@@ -0,0 +1,24 @@
+
+allprojects { prj ->
+  plugins.withType(JavaPlugin) {
+    prj.apply plugin: 'com.diffplug.gradle.spotless'
+
+    spotless {
+      java {
+        licenseHeaderFile rootProject.file("gradle/validation/spotless/source-header.txt")
+        lineEndings 'UNIX'
+        endWithNewline()
+        googleJavaFormat('1.8')
+      }
+
+      check.dependsOn(spotlessCheck)
+    }
+
+    task tidy() {
+      description "Applies formatters and cleanups to sources."
+      group "verification"
+
+      dependsOn spotlessApply
+    }
+  }
+}